I think city maintenance is a little too steep. Where can I find the values to adjust this?

The easiest would be Civ4HandicapInfo.XML or Civ4WorldInfo.XML (both in the GameInfo folder) where you can set a percentage of the maintenace cost for a difficultie level or for a world size.

Relevant tags are (in both files)
iDistanceMaintenancePercent,
iNumCitiesMaintenancePercent

Note that the Handicap file has separate tags for you and the AI (the later having AI in the tag's name), so you need to adjust both, IF you want to play fair :D